Глава 8

Наложение и позиционирование карт

Введение

You can scale each map as it is created and position it on the page at any location by dragging it with the mouse.

Combining Maps and Creating Overlays

You can combine several maps of related data by overlaying the maps. You can overlay any combination of base maps, contour maps or post maps, but overlays can contain only one surface plot. When you overlay maps, the overlays use a single set of X, Y, and Z axes, and the maps are positioned according to the coordinate systems used by the maps. If two or more maps use the same coordinate limits they will overlay on top of one another. If you have several maps that cover adjacent areas, overlaying maps places them in the correct position relative to one another and creates a single set of axes encompassing the entire group. Map overlays can be moved as a single object on the page.

Consider a case where you have a contour map and a base map used to draw the outline of a lake on the contour map. The limits of the base map are the XY extents of the lake and are most likely not the same as the contour map limits. If you create both the base map and the contour map in a single Plot window they do not overlay correctly because the maps are scaled differently by default. Also, each map uses a different set of XY axes. If you select both maps and then choose the Overlay Maps command, the contour map and the base map are resealed and combined into a single map using a single set of axes. The lake will now be correctly positioned on the contour map.

Overlays consist of two or more maps combined into a single composite map, but you can stillmodify each of the individual maps within the overlay. For example, you might combine a surface plot and a contour map into an overlay, and want to change the contour Hntervals on the contour map. You can select the contour map from the overlay and modify the contour levels displayed, without otherwise affecting the overlay.

When you select maps in an overlay, the map on top is the first selected. The selected map from the overlay is indicated by the text in the Status Bar. If you want to select a map that is not on top, hold down the CTRL key on the keyboard and click until the desired map is selected. When the map you want is selected, double-click to display the dialog box for that map. Alternatively you can click the overlay and choose the Edit Overlay command from the Map menu. In the Edit Components dialog box, select the desired map and click the Edit button. This also displays the dialog box for the selected map.

When you overlay contour, post or base maps on a surface plot, the maps area draped over the surface. The surface map is drawn in the usual fashion but the base or contour maps are molded’ over the top of the surface. For example, you can create a surface plot and then overlay a basemap, contour map,. post map or classed post map on a surface plot.

Hidden lines are not removed from maps overlaid on surface plots. For example, the contour map contour lines that are behind other lines are not hidden when the contour map lies over a surface plot. When you overlay a filled contour map on a surface plot, it is advisable that you use the invisible line style for the contour lines on the contour map. See the Assigning the Same Line Attributes to all Contour Levels section of Chapter 6 -Contour Maps for more information on assigning line styles on contour maps. The invisible line style is the blank box in the Styles palette of the Line Attributes dialog box.